In recent years, position-control stage systems have been needed to be compact or slim in construction and able to operate with high speed and high response to make sure of high speed movement and accurate position control so as to meet anticipated design requirements in extensively increased fields including semiconductor industries, and the like.
The prior position-control stage system is in general provided therein with an onboard permanent-magnet motor that is comprised of a primary side having armature windings and a secondary side having field magnets, the armature windings being made of three-phase coreless windings wound in annular flat configuration and arranged on a stationary bed in juxtaposition with one another along a circular pattern of a preselected radius of curvature in a way each of which is oriented in a radial direction of the circular pattern. The prior position-control stage system constructed as stated earlier is envisaged making it easier to extend largely an angular movement in circular direction for position control, rendering the position-control stage system itself compact or slim in construction, allowing the position-control stage system to work with high precision in clean environment and further produce the stage system with inexpensive cost. An example of the prior position-control stage systems as stated earlier is disclosed in, for example Japanese Patent Laid-Open No. 2004-72960 in which there is installed an onboard motor made up of the primary side having armature windings and the secondary side having field magnets. The armature windings are made of three-phase coreless windings wound in annular flat configuration. The armature windings are arranged on a stationary bed in juxtaposition with one another along a circular pattern of a preselected radius of curvature in a way each of which is oriented in a radial direction of the circular pattern. Magnet segments to provide a field magnet are each made in a rectangular shape. The magnet segments are oriented in radial direction respectively and disposed on a turntable in opposition to the armature windings in a way alternating in polarity circularly.
Disclosed in for example Japanese Patent Laid-Open No. 2002-328191 is a stage system with an onboard linear motor, in which just tiny angular position-control may be performed by virtue of the linear motor. The prior stage system is made smaller in construction as well as reduced in the overall height and also improved in response to high-speed operation. The prior stage system is comprised of a first stage lying on a base stage for linear movement in an X-direction relatively to the base stage, a second stage lying on the first stage for linear movement relatively to the first stage in a Y-direction, a turning stage supported on the second stage through a rolling-contact bearing, and a linear motor causing the turning stage to move angularly towards any desired position over a tiny angle in circular direction.
Another Japanese Patent Laid-Open No. H05-91710, moreover, disclosed a motor for swinging motion, which is comprised of even permanent-magnet segments for field magnet positioned in a circular direction at regular intervals in a way alternating in polarity circularly around a rotating axis, and armature windings equal in number with the poles of the permanent-magnet segments and lying in opposition to the permanent-magnet segments. Either of the permanent-magnet segments and the armature windings serves as the stator while the other is the rotor in a construction that a yoke is always set on the side of the stator. Moreover, the armature windings to create the propulsion are made equivalent in number in conformity with the number of the permanent-magnet segments for the field magnet to make the motor simple in construction. More specially, the number of the armature windings is selected to an even number as small as allowed so long as ensuring the desired propulsion.
The prior position-control stage systems constructed as stated earlier, although but having been made measurably compact in construction, nevertheless, are thought to still remain even larger in size. With these prior position-control stage systems constructed as stated earlier, moreover, the armature windings are made in annular rectangle in configuration while many magnet segments for the field magnet are also made rectangular in shape in order for the manufacturers to utilize versatile components for the linear motors in other linear motion guide units in favor of the stage systems inexpensive in production cost. That is to say, the prior position-control stage systems recited above have required many armature windings for the armature assembly and many magnet segments for the field magnet to generate propulsion desired to turn the turntable. The armature windings and the magnet segments have been both positioned in circular direction. This circular construction of the armature windings and the magnet segments results in rendering the stage systems large or bulky in contour or in outside diameter thereof. Thus, it remains a major challenge to make the position-control stage system much smaller in construction, even with enhancing propulsion desired to turn a turntable. Moreover, the motor for swinging motion constructed as recited earlier, because of envisaged making position control of the magnetic head in the magnetic disc unit, would be unfit in construction for the stage system to control the workpiece, mounted on the stage system, in circular position.